The present invention relates to an injection device capable of delivering multiple doses of a liquid medicament contained therein without the need to refill the device between doses.
Various types of drug treatments, including hormone therapy and the like, require administration of the drug-containing liquid medicament at regular intervals over an extended period of time. For example, a specific hormone treatment can require daily administration of the drug for a period of thirty days. In such a situation, it is advantageous to provide a device that allows the patient to self-administer the injection to avoid repeated trips to a doctor's office or the like.
Various injection devices have been developed that allow self-administration of multiple doses of medication. For example, U.S. Pat. No. 4,592,745 provides an injection device that includes a unidirectional transmission mechanism that advances a piston rod in successive axial steps based on advancing axial movement of a pressure device. Similarly, U.S. Pat. No. 3,790,048 discloses an injection device that uses a cam barrel and a ratchet to translate actuation of a trigger to cause advancement of a plunger and to cause the plunger to remain stationary during repositioning of the trigger. In both of these devices, the reciprocal motion of the trigger is such that the return stroke follows the same path as the dosing stroke, but in an opposite direction.
U.S. Pat. No. 6,562,006 discloses a device that uses rotation of the trigger to reset the device for successive dosing. Another reference describes a device that is also adjustable between a priming dose and an injection dose. The dosing of these devices is selectable by the user, which can allow errors in selecting the dose, potentially reducing the efficacy of the medication or leading to harmful side effects.
U.S. Patent Application Pub. No. 2007/0088288 describes a device that allows a user to administer a fixed dose of the liquid medicament contained therein. The device does not use a reduction mechanism, but rather has a trigger that disengages from the piston rod when depressed to give the user a feeling of a longer trigger motion.
A device is needed that allows for repeated administration of a dose of medicament that is easy to use correctly in self-administration.